1. Field of the Invention
This invention relates to ceiling suspension systems of the type having longitudinally extending runners and transverse cross runners forming openings for receiving and supporting panels or fixtures, and more particularly to such a system adapted for the intersection of an end of a cross runner with an intermediate part of a main runner and the absence of corresponding cross runner at the opposite side of the main runner. Such an intersection will be referred to as an "ashlar" condition or configuration.
2. Prior Art
Suspended ceiling system are well known and widely used. Usually, these systems have elongated main runners and cross runners in the form of inverted tees which are suspended from structures above by wires in a grid arrangement. The main runners are parallel and spaced with cross runners extending transversely therebetween forming grid openings. Ceiling panels, light fixtures or the like are placed in the openings supported by the flanges of the runners. The main runners have slots or openings in their vertical webs where the cross runners intersect therewith, and the cross runners have connectors on their ends which extend through the slots and mate with colinear cross runners on the opposite sides of the main runners.
An example of such a conventional system is shown in U.S. Pat. No. 4,108,563. Connector clips are attached to the ends of mating cross runners, these clips being inserted from opposing sides through a vertical slot in the web of the main runner. The connectors are formed with tabs and slots which engage each other and the web of the main runner to resist forces tending to pull out the cross runners. The combination of these interconnections makes the structure highly resistant to pull-out forces.
It may desired to install a suspended ceiling system where some or all of the intersections are in the ashlar condition, i.e., there being a single cross runner at points of intersection with the main runner. However, such installations must still meet the requirements of building codes, including adequate pullout strength to resist forces caused by seismic disturbances. The mere modification of conventional grids by omitting cross runners at intersections will usually result in insufficient pullout strength. The slots in the main runners, which were designed for the insertion of two connectors, will be too loose for a single connector. Furthermore, with the absence of an interconnection with an opposing cross runner, there will be less resistance to pullout forces and increased stress on the web of the main runners near the slots, possibly resulting in failure of the web.